This invention relates in general to a seating system for treating sit complaints and sit impairments, especially decubitus ulcers.
The body-weight functions as an acting force when lying down and sitting. This force is distributed over the contact area that the body has with the supporting surface. The quotient of force and contact area is pressure, as shown in FIG. 1. The larger the contact area the lower the local pressure. A pressure value less than 60 mmHg seldom causes complaints or impairments. A pressure greater than 60 mmHg usually results in an awareness of pain when the pressure is sustained over a longer period of time. Regularly changing the lying or sitting position reduces or prevents pain. However, a pressure greater than 100 mmHg compresses the subcutaneous micro-circulation. This can lead to irreversible skin or soft tissue damage, resulting in decubitus ulcers. Actually, the pain and decubitus, or a threat of decubitus, is not so much an expression of excessive pressure, but more of excessive local loading, which is expressed as the product of pressure and time.
In sitting, the acting force (i.e., the body-weight) is not usually applied perpendicularly but at an angle to the supporting surface and therefore a shear force is generated, as shown in FIG. 2. Because of this non-perpendicular loading people have the tendency to slide away. An abnormal sitting position can be prevented by active posture correction, which is based on the capability of a person to execute motor control over body functions (e.g., joints, muscles, etc.). In patients with no or a decreased capability of motor control over the body functions (e.g., joints, muscles, etc.) sitting and lying becomes a problem and causes complaints.
The potential efficacy (i.e., a non critical load and adequate sit stability) of wheelchair seating systems can be derived from above mentioned biomechanical starting points of local deloading and stabilizing of the body in place. In general, patients with wheelchair sit-complaints/impairments are treated with a standard sit-cushion. When this treatment is not successful, unless some alternative treatment is applied, this leads to chronic recitative wheelchair sit complaints.
Standard sit-cushions and backrests are manufactured (in series) as off-the-shelve products. The following are characteristics/limitations of present standard sit cushions not anatomically (i.e., three dimensional) shaped, or limited anatomical shape; not specifically designed for/suitable for an unequal load distribution over the buttocks; not specifically designed to achieve pelvic stability; and not specifically designed to compensate sit pathology.
The characteristics/limitations of the present standard sit cushions frequently cause the situation that treatment of wheelchair sit complaints/impairments via standard sit cushions do not deliver a positive medical treatment result, in other words lead to chronic/recitative sit complaints/impairments.